Thermometer



K. L. TATE THERMOMETER June 23, 1931.

Filed Dec. 2 1928 b w H a a m M 44 N 0 3 W. m N & l J B 4 .6 a x 4 Patented June 23, 1931 i'JNrrED STATE rAraNroI-rics KENNETH L. TATE, OF ROCHESTER, NEW YORK ASSIGNOR TO TAYLOR INSTRUMENT COMPANIES; OF ROCHESTER, NEW YORK, A. GOR PORAT'ION OF NEW YORK snnmroma'ran' Application filed December 27, 1928. Serial No. 328,772.

This invention relates to thermometers having a glass stem defining a capillary bore containing mercury as the thermal indicating medium.

[ Heretofore devices of this type have been limited almost exclusively to constructions wherein the bulb and the stem are one integral piece of glass. It was heretofore considered impractical, if not practically impossible to provide glass thermometers of the distance thermometer type, i. e., thermometers comprising a glass stem of the usual form and a bulb removed a considerable distance away from the stem. 4 s

The reason for the general absence of distance glass thermometers in industrial and commercial application is probably due to the fact that for distance transmission a capillary tube of metal is required, which can be 2 connected with the glass stem only with difficulty and by methods which are expensive and more or less unsatisfactory, since the coefiicients of expansion of metal on the one hand, and of glass, on the, other hand, dif

fer widely, with the result that unequal expansion and contraction area potential cause of destruction of the thermometer, and, in fact, makethe glass stem very 'susceptable to breakage.

It is the general object of this invention to rovide a glass distance thermometer which is free from the objection referred to.

Another-object of the invention is a glass distance thermometer which may be cheaply 85 manufactured.

For a full understanding of-the' invention, its characteristic features and its execution, reference is made to the accompan ing drawings which form part.of the speci cation.

- In the drawings:

Fi 1 is a face view of a thermometer embodying the invention; Fig. 2 is a fragmentary section, on an enlarged scale, showing the material part of the invention 5 Fig. 3 is a similar view showing a modifica-' tion of the form shown in Fig. 2; and

Fig. 4 is a sectional view ofa detail showin another modification." y W the drawings lrepresents the stem of a glass thermometer, 2 a bulb and 3 the capillary. k

The capillary 3 is composed of two tubular bodies, an inner layer 3a and an outer layer 3?). The inner tube 3a is composed of 5 some metal which is immune against the action of mercury and the outer tube 36 is of a metal so chosen that the resultant coeflieient of ex ansion of the tube as a wholeis substantial y that of glass. or, more in parso ticular, of the glass of the stem.

\Vhile there is a certain degree of latitude as to the materials available for the purpose stated, ll prefer invar steel as the metal for" the inner tube and copper for the outer tube.

The proportion of invar and copper depends on various factors," such as the composition of the invar and the modulus of elasticity of the two metals and glass, respectively, but it is approximately 2: 1 i. e., two parts of invar to one part of copper.

The capillary may be produced in several ways, as for instance by welding sheets of invar and copper together, cupping the compound sheet and drawings down to the required-size or by welding a copper tube upon an invar rod, drilling the rod and drawings down to the required size.

The finished capillary is then attached to the glass stem much as the lead-in wire is go embedded in incandescent light bulbs, the outer surface ofthe tubing being preferably coated with borax before the glass stem is pressed on to it'in plastic condition.

In order to prevent contact between the 35 mercury and copper, the capillary is so'prepared that only invaris exposed to the mercury at the end of the capillary in the glass tube. This may be readily accomplished in various ways. I

Having reference to Fig. 2, the end of the copper layer may be removed to expose the portion 4 of the layer 3a. When the capillar-5 has been placed into the end of the stem an the glass is heated up and pressed as around it, the operation ma be so conducted as to force the glass over the end surface of the layer 36 and close to the surface of the exposed layer 3a, as indicated. Due to the surface tension of mercury, the latter does 10(- not flow into the minute clearance space which may be left between the layer 3a and the glass. As indicated in Fig. 3, the exposed layer I 5 3a may be swaged outwardly to define a thin edge 4a. With this provision, the glass may i be pressed practically into contact with the edge 4a, since upon contraction of the glass, the edge 4a yields sutliciently to avoid breakage of the glass. The edge 4a thus forms a seal against ingress of mercury into the space below the edg4a and into contact with the copper layer.

Fi 4 shows the end of the layer 3a swaged or otierwise forced over the end surface of the layer 3a, except for a minute portion to leave a slight clearance between the glass and the surface40. The cap 4b thus formed substantially covers the end surface of the copper layer 3b and the mercury cannot come into contact with the latter.

The combination of metals for making the compound tubing should be such that the metal in contact with the glass has the propertly of wettingthe latter.

claim: I 1. In a mercury thermometer, the combination of a glass stem having a capillary bore and terminatin in an enlarged bore, a

capillary tubing embedded in the enlarged bore, said tubing consisting of an inner layer of a metal immune to mercury and an outer layer of a metal of such character and such thickness relatively to the inner layer that the coefiicient of expansion of the tubing as a whole is substantially that of the glass of the stem, the inner layer at the end of the tubing in the stem extending beyond the end of the outer layer and forming with the in- 0 ner surface of the glass a seal against contact of the mercury with the outer layer.

2. In a mercury thermometer, the combination of a glass stem having 9. ca illary bore and terminating in an enlarged ore, a

5 capillary tubing embedded in the enlarged bore, said tubing consisting of an inner layer of a metal immune to mercury and an outer layer of a metal of such character and such thickness relatively to the inner layer. that the coefficient of ex ansion of the tubing as a whole is substantially that of the glass of the stem, and means at the end of the tubing in the stem for preventing contact between the outer layer and the mercury,

In testimony whereof I afiix my signature.

KENNETH L. TATE.

CERTHFHCATE COGTION.

mew. 1,811,190; Granted June 23 1931, w

KENNETH L. TATE.

It is hereby certified that ermf appears in the printed specification of the above numbered patent requiring eorrectien as fellows: Page H lines 75 d W;

' for the word "drawings" read drawing; and that the said! Lefiters Patem should be 1; read with these correetions thereie that me samemay maxim-m to the Fecord eff the case in the Patent 0mm,

Signed and sealed this 4th y of st, A. R. 19311.

.. A, Meme, 

